Zooplankton taxa exhibit varying tolerances to UV radiation (UVR), with rotifers and copepods tending to be more UV tolerant than cladocerans. Based on these differences, we hypothesized that UV avoidance behavior would be greatest in zooplankton with low UV tolerance. Both downward and upward movements of zooplankton were examined in cylindrical acrylic columns that either transmitted full solar radiation (UV+ treatment) or blocked UV-B and short wavelength UV-A radiation (UV- treatment). Columns were suspended in the surface waters of a high UV lake at varying times of day and cloud cover.
Rotifer and copepod swimming patterns were similar in both the UV+ and UV- treatments, suggesting no UV avoidance behavior. Cladocerans, however, displayed a distinct avoidance of the surface waters in the UV+ treatment but often showed a preference for the surface in the UV- treatment. These observed patterns suggest that UVR may potentially influence the vertical distribution of zooplankton in high UV lakes.